High Rpm misfire
12-08-2006, 03:37 PM
#1
Teching In
Thread Starter
Join Date: Oct 2005
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
High Rpm misfire Little background on the car I have changed the plugs they should be all good so are my plug wires. I took my car to the track and couldn't get it to 6k without crazy misfires. It pulls great until about 5 then cuts starts popping. I have a tune by Madz28. Could it be not enough fuel bad tune hitting rev limiter?
I am kinda lost cause the car runs good up until 5k.
I am kinda lost cause the car runs good up until 5k.
12-08-2006, 04:46 PM
#2
same situation for me in the past, turned out to be a bad opti, the bearing sensor bearing was shot completely and the rotor was somewhat worn. Changed it with new plugs and new 02 sensors, ran perfect. Hopefully that helps a little.
12-08-2006, 05:15 PM
#4
Teching In
Thread Starter
Join Date: Oct 2005
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
Just took it out again and now it misfires even lower like at 4k the problem was definately worse. Could it be just the cap of the Opti probably not. Also could this be early signs of Opti failure and my car might not crank up one day it is my DD.
12-08-2006, 05:18 PM
#5
Teching In
Thread Starter
Join Date: Oct 2005
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Cammed95Z28
I have the same problem and I'm thinkin injectors on mine...
12-08-2006, 07:37 PM
#6
Probably opti cap on most of them. High RPM misfires. Seen it a million times. If the opti shaft feels good and the reluctor looks good, its the cap. Incidently, its high secondary resistance from A: worn plugs, excess gap, or B: High resistance wires, which where probably caused by increased plug gap, that kills the caps. They end up misfiring thru the epoxy because of the rerouting.
We rarely see the actual electronic module in them go bad. Its the Caps with the highest failure rate, followed by bearing failure,second most common, which ends up screwing them up completely.
We rarely see the actual electronic module in them go bad. Its the Caps with the highest failure rate, followed by bearing failure,second most common, which ends up screwing them up completely.
12-08-2006, 09:57 PM
#7
Had a very small inconsistant stumble at 5.5K RPM. After engine tear down and dissecting the opti I found the two rotor screws half way backed out. Clearly the rotor was not secured which had to have some ill side affect plus there was a weird mark on the top of the cap that looked like a burn. The springy terminal on the top was doing all the work holding things together. From now on I lock-tite these and highly reccomend this to every LT1 owner out there.
Others have claimed that the loose rotor can cause this problem too. Cap is also plausable, however I have a lot of confidence in the reat of the opti.
Others have claimed that the loose rotor can cause this problem too. Cap is also plausable, however I have a lot of confidence in the reat of the opti.
Trending Topics
12-09-2006, 12:27 AM
#8
Teching In
Thread Starter
Join Date: Oct 2005
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by edcmat-l1
Probably opti cap on most of them. High RPM misfires. Seen it a million times. If the opti shaft feels good and the reluctor looks good, its the cap.
12-09-2006, 01:05 AM
#9
On The Tree
Join Date: Jan 2006
Location: Leander, TX
Posts: 161
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by slow_94z
Can you just buy a Opti cap? I guess there is no rotor in there like other distributors. Also how do I check or tell if the "opti shaft feels good and the reluctor looks good".
Its best to replace the whole thing. Do it right and spend the money on the MSD, you won't regret it.
12-09-2006, 04:12 AM
#10
Teching In
Thread Starter
Join Date: Oct 2005
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Cammed95Z28
Its best to replace the whole thing. Do it right and spend the money on the MSD, you won't regret it.
Who sells them and I gotta ask why not a stock replacement I am still going to do few things to the car before replacing Opti. How common does the ICM go out anbd could and 02 effect misfires anyone?
Last edited by slow_94z; 12-09-2006 at 04:18 AM.
12-09-2006, 07:19 AM
#11
Wait! before you go spending a boat load on a new opti, check to make sure you coil isnt weak. If its weak it will feel like your hitting the revlimiter. My car did the exact same thing and it turned out to be a weak ignition coil. Its alot cheaper and way easier to replace. It would really suck to spend money on a new opti then put it all back together again and still be left with the same problem. Not saying it isnt the opti, I would just check the coil out first. This happens all too often!
12-09-2006, 07:47 PM
#13
Originally Posted by slow_94z
Who sells them and I gotta ask why not a stock replacement I am still going to do few things to the car before replacing Opti. How common does the ICM go out anbd could and 02 effect misfires anyone?
12-09-2006, 08:49 PM
#14
12 Second Club
iTrader: (5)
Join Date: Jul 2006
Location: Tampa, Fl
Posts: 583
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by infinitebird
The coil/icm going out is fairly common at higher miles, and if it still misfires at wot, it's not the o2s most likely.
The O2 readings are only used when the car is running in closed loop. At open loop (WOT) it isn't using the O2 readings anymore.
Closely inspect all of the plug wires. Also I second looking into replace the ignition coil and checking the ICM. Those two could also be causing sputtering at high rpms.
Another thing to consider (and possibly an easy fix) is to look into replacing your fuel filter as well. If you can't remember the last time it was replaced, it definately won't hurt to do that either.
..
06-04-2011, 11:01 PM
#16
Launching!
iTrader: (20)
Join Date: Jun 2005
Location: Clarksville, MD
Posts: 264
Likes: 0
Received 0 Likes
on
0 Posts
I think I have this problem, ocassionaly misfire at 5500+ rpm. It appears to only be doing it while hot. I have had sucess in having it work problem free right after starting. I will try shbox's icm cooling modification to see if this solves the problem permanently. I was about to do the optispark but I decided not to. I will be changing the optispark harness because the opti-end was slightly cracked/corroded. If all else fails I'll change the coil and worst case the opti. Already have good plugs and wires. The fuel filter was changed recently as well.
06-04-2011, 11:03 PM
#17
Launching!
iTrader: (20)
Join Date: Jun 2005
Location: Clarksville, MD
Posts: 264
Likes: 0
Received 0 Likes
on
0 Posts
I think I have this problem, ocassionaly misfire at 5500+ rpm. It appears to only be doing it while hot. I have had sucess in having it work problem free right after starting. I will try shbox's icm cooling modification to see if this solves the problem permanently. I was about to do the optispark but I decided not to. I will be changing the optispark harness because the opti-end was slightly cracked/corroded. If all else fails I'll change the coil and worst case the opti. Already have good plugs and wires. The fuel filter was changed recently as well.
